Method and apparatus for the reading of a bar code

1. A method of reading a bar code consisting of a predetermined number of code elements for generation of a binary signal with sequential high and low phases, the lengths of which correspond to the width of the sequential code elements, the method comprising: sensing the code elements by one or more sensing beams of a bar code reader along scanning lines extending substantially parallel to one another, wherein each region of a code element sensed by a scanning line forms a code element section; detecting, for substantially each scanning line, those codes segments that consist of a code element section or a plurality of sequential code element sections, which are recognized as permissible code segments on the basis of preset decision criteria; finding in each case a reference code element from mutually associated code element sections, each representing the same code element of the bar code for different scanning lines; storing detected permissible code segments in an image memory; after the detection and storing of the permissible code segments, freeing of distortion the segmented image of the bar code deposited in the image memory for allowing the forming of the reference code element; determining a shift between code elements detected for two adjacent scanning lines; shifting each code segment stored for a certain scanning line within the image memory by such an element of said shift that corresponds to the distance of said certain scanning line from said two adjacent scanning lines; and producing the binary signal from the reference code elements.

2. A method in accordance with claim 1, wherein a shift present in the scanning direction between code segments detected for different scanning lines, and arising as a result of a scanning direction extending obliquely to the code elements, is evaluated in the sense that respective code element sections detected for different scanning lines are used correspondingly shifted relative to one another as the mutually associated code element sections.

3. A method in accordance with claim 2, wherein the shift is determined with respect to a straight reference line extending substantially perpendicular to the scanning lines.

4. A method in accordance with claim 1, wherein the mutually associated code element sections respectively detected for different scanning lines are determined by calculation of lines of regression for at least one of the start and end of the respective code element sections.

5. A method in accordance with claim 1, wherein at least one of the start and the end of the bar code is determined by means of predetermined start and/or stop patterns provided in the bar code.

6. A method in accordance with claim 5, wherein the detection of the admissible code segments starts when the start pattern and/or stop pattern is recognized for at least two adjacent scanning lines.

7. A method in accordance with claim 5, wherein the detection takes place for the scanning line containing the first recognized start and/or stop pattern and also for the scanning lines following it.

8. A method in accordance with claim 5, wherein the detection of the permissible code segments is terminated when a stop and/or start pattern corresponding to the recognized start and/or stop pattern has been recognized a plurality of times.

9. A method in accordance with claim 1, wherein the detection of the permissible code segments starts when substantially identical code segment sections are recognized for at least two sequential scanning lines.

10. A method in accordance with claim 5, wherein the shift between the code segments detected for different scanning lines is determined by the shift between the start patterns recognized for the corresponding scanning lines.

11. A method in accordance with claim 5, wherein the shift between the code segments detected for the different scanning lines is determined from the shift between the stop patterns recognized for the corresponding scanning lines.

12. A method in accordance with claim 1, wherein no permissible code segment is present when a minimum width of a scanned element in the scanning direction falls below a permissible minimum width.

13. A method in accordance with claim 12, wherein the permissible minimum width is determined in dependence on at least one of the reading distance and the print resolution of the bar code.

14. A method in accordance with claim 1, wherein no permissible code segment is present when a maximum width of a sensed element in the scanning direction exceeds a permissible maximum width.

15. A method in accordance with claim 14, wherein the permissible maximum width is determined in dependence on at least one of the reading distance and/or the print resolution of the bar code.

16. A method in accordance with claim 1, wherein no permissible code segment is present when, on using a two-width code, a ratio of sensed elements is greater than 3:1 or smaller than 1:3.

17. A method in accordance with claim 1, wherein no permissible code segment is present when, on using a multi-width code, a ratio of sensed elements is greater than 4:1 or smaller than 1:4.

18. A method in accordance with claim 1, wherein no permissible code segment is present when the running length or number of elements of the code segment falls short of a predetermined minimum length or minimum number.

19. A method in accordance with claim 1, wherein no permissible code segment is present when the running length or number of elements of the code segment exceeds a predetermined maximum length or a predetermined maximum number.

20. A method in accordance with claim 5, wherein the start pattern is formed by a white zone, with the ratio between the width of the white zone in the scanning direction and the width of the subsequent code element being greater than a predetermined minimum value.

21. A method in accordance with claim 5, wherein the stop pattern is formed by a white zone, with the ratio between the width of the last code element and the width of the subsequent white zone in the scanning direction being smaller than a predetermined minimum value.

22. A method in accordance with claim 5, wherein the start pattern is formed by a start marking provided in the bar code.

23. A method in accordance with claim 5, wherein the stop pattern is formed by a stop marking provided in the bar code.

24. A method in accordance with claim 1, wherein the bar code is decoded from the binary signal, which is produced from the reference code elements.

25. A method in accordance with claim 1, wherein the bar code is decoded from the binary signal, which is produced from the code segment detected for one scanning line when the length of the detected code segment is substantially the same as the running length of the bar code.

26. A method in accordance with claim 1, wherein in each case, the width of a reference code element is determined by forming the average value of the widths of the corresponding, mutually associated code element sections detected for the different scanning lines.

27. A method in accordance with claim 26, wherein an arithmetic average value is formed.

28. A method in accordance with claim 26, wherein a median value is used as the average value.

29. A method in accordance with claim 1, wherein the reference code elements are stored in an image memory.

30. A method in accordance with claim 1, wherein the scanning lines have a substantially equidistant spacing from one another.

31. An apparatus for reading a bar code consisting of a predetermined number of code elements for the generation of a binary signal with sequential high and low phases, the lengths of which correspond to the width of sequential code elements, in particular with a reading direction extending obliquely to the code elements wherein a bar code reader which transmits one or more scanning beams for the sensing of the code elements along scanning lines extending substantially parallel to one another, wherein each region of the code element sensed by a scanning line forms a code element section, a code segment selection means is provided for the determination of permissible code segments as a result of predetermined decision criteria and consisting of one code element section, or of a plurality of sequential code element sections, a code segment detection means is provided for the detection of the code segments recognized as permissible by the code segment selection means for substantially each scanning line, by a reference code element determining means for determining in each case a reference code element for respective, mutually associated code element sections representing the same code element of the bar code and detected for different scanning lines, an image memory for storing the detected, permissible code segments, a shift determining means for determining the shift between two code segments detected for two adjacent scanning lines and stored in the image memory, a code segment shifting means for shifting within the image memory a code segment stored in the image memory for a certain scanning line by such a multiple of said shift which corresponds to the distance between said certain scanning line from said two adjacent scanning lines, and a signal generating means is provided for the generation of the binary signal from the reference code elements.

32. A method of reading a bar code consisting of a predetermined number of code elements for generation of a binary signal with sequential high and low phases, the lengths of which correspond to the width of the sequential code elements, the method comprising: sensing the code elements by one or more sensing beams of a bar code reader along scanning lines extending substantially parallel to one another, wherein each region of a code element sensed by a scanning line forms a code element section; detecting, for substantially each scanning line, those codes segments that consist of a code element section or a plurality of sequential code element sections, which are recognized as permissible code segments on the basis of preset decision criteria; finding in each case a reference code element from mutually associated code element sections, each representing the same code element of the bar code for different scanning lines; carrying out a two-dimensional Fourier transform of the detected code segments and determining the maximum amplitudes of the spectrum of magnitude that is found; determining the tilt angle between the scanning direction and the direction perpendicular to the bar orientation of the bar code from the position of the maximum amplitudes; calculating the shift between the code element sections respectively detected for different scanning lines from the tilt angle; compensating the shift; and producing the binary signal from the reference code elements.

33. A method in accordance with claim 32, wherein a shift present in the scanning direction between code segments detected for different scanning lines, and arising as a result of a scanning direction extending obliquely to the code elements, is evaluated in the sense that respective code element sections detected for different scanning lines are used correspondingly shifted relative to one another as the mutually associated code element sections.

34. A method in accordance with claim 4 wherein the mutually associated code element sections respectively detected for different scanning lines are detected for sequential scanning lines.

35. A method in accordance with claim 16 wherein the ratio of sensed elements is a ratio of sequential sensed elements.

36. A method in accordance with claim 17 wherein the ratio of sensed elements is a ratio of sequential sensed elements.

37. A method in accordance with claim 19 wherein a predetermined maximum length is a running length of the bar code.

38. A method in accordance with claim 1 wherein the width of the sequential code elements corresponds to a reading direction extending obliquely to the code elements.

39. A method in accordance with claim 32 wherein the width of the sequential code elements corresponds to a reading direction extending obliquely to the code elements.